Solid State Dewetting-Mediated Aggregation of Particles

Palmer, Jacob S.

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Description

Title

Solid State Dewetting-Mediated Aggregation of Particles

Author(s)

Palmer, Jacob S.

Issue Date

2008

Doctoral Committee Chair(s)

Weaver, John H.

Department of Study

Materials Science and Engineering

Discipline

Materials Science and Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Engineering, Materials Science

Abstract

• Structure assembly on surfaces is a field of intense research because of its potential for building devices and device arrays at the nanoscale. An important issue for such assembly is the interaction between the structure material and the surface, since these interactions impose severe restrictions on both structure formation and assembly. A novel and robust way of circumventing the growth restrictions of atomic depostion onto a surface is buffer-layer-assisted growth (BLAG). In BLAG, clusters are formed spontaneously when atoms of a material of choice are vapor-deposited onto a thin buffer layer, which is subsequently removed to deliver the structures formed on the buffer to the substrate. Typical buffers consist of thin layers of rare gas solids that have been grown at 20-50 K. The properties of the resulting structures are dependent on the interaction of the deposited species with the buffer rather than with the substrate, making possible a wide range of nanostructure/support systems that cannot be formed by conventional deposition techniques. The size, shape, and number density of the structures can be controlled by varying the amount of material deposited and the thickness of the buffer layer.
• Previously, the BLAG process was described in terms of a diffusion-limited cluster-cluster aggregation process during layer-by-layer desorption of the buffer. We present evidence that significant diffusion, restructuring, and dewetting occurs prior to desorption for Xe buffers on a-C and this leads to Au particle aggregation. Particle motion and aggregation is driven by capillary forces as the dewetting film retreats and sublimes.
• Xe condensed on a-C and SiOx exhibit an island growth mode and results in kinetically-stabilized polycrystalline films. Heating to desorb the buffer results in grain boundary grooving and void formation. Particles move with the dewetting front as the voids grow, leading to the formation of larger aggregates. The presence of nanoscale particles on the film inhibits dewetting and significantly alters the shape of the front. Kinetic Monte Carlo simulations reproduce the experimentally observed particle shapes and size distributions, and they provide additional insight into the interaction of the particles with the dewetting front.
• This particle aggregation process is not limited to particles deposited onto condensed noble gas films. It shares similarities with the drying-mediated assembly of nanostructures that occurs during solvent evaporation as particles are left behind, as well as with the dewetting and islanding of thin metal and polymer films during annealing. The solid state dewetting-mediated assembly of structures also occurs for BLAG with CO2 and H2O layers. In contrast to Xe or CO2, the structure of the solid water depends strongly on the deposition kinetics. While some details of dewetting and the interaction of particles with the film are different, the aggregation process is still driven by the dewetting, islanding, and sublimation of the ice films. The sizes, shapes, and densities of the resulting nanostructures are determined by the formation of ice islands whose sizes and densities are controlled by the thickness of the ice film.

Graduation Semester

2008

Type of Resource

text

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